The invention relates to a shaft and a ring for sealing radially thereabout.
A known seal ring is produced from a planar, annular disk of a non-elastomeric plastic, preferably polytetrafluoroethylene. The outer circumference of the disk is held about a shaft in a stiffening ring and the inner circumference of the disk is cold flexed about the shaft in the direction of the space to be sealed to form a cylindrical stub which engages the shaft under bias.
German Federal patent publication OS No. 25 53 290 describes a seal ring of the above kind. Its planar, annular disk has ribs projecting inwardly from its cylindrical-stub portion and contacting the shaft for pumping back any leakage. For this reason, attaining good sealing action depends on the shaft turning at the correct speed.
If the circumferential speed of the shaft is too great, so is the pumping action of the ribs. This can cause lubrication failure around the dynamic sealing zone of the ribs as well as the pumping of dust from the surroundings into the dynamic sealing zone and even into the sealed chamber. These events are undesirable and can result in the premature failure of the seal.
If the circumferential speed of the shaft is too small, so is the pumping action of the ribs. This shifts the dynamic sealing zone toward the outside, away from the sealed chamber, especially in the interstices between the individual ribs, which causes undesirable contamination. Particularly when the shaft is at rest, and in cases in which pressure builds up in the sealed chamber, this effect is plain to see.